1. Field of the Invention
The present invention refers to a breather bag made with an impermeable and flexible membrane and having an appropriate shape, for use in open type or closed type tanks for storage and/or transportation of liquid products under atmospheric pressure. Specifically, the present invention refers to a bag that is produced by using a membrane that, working as a breather in a storage tank, guarantees that the air vent of the storage tank will work normally, without discharacterization of its qualification in storage and/or transportation of liquid products under atmospheric pressure. Additionally, it makes possible the operation of air venting in storage tanks with physical segregation between the stored liquid product and the atmospheric air and environment.
2. Description of Related Art
As it is well known, a storage tank is of an atmospheric type when its inner side communicates with the environment (atmosphere) by a free way (air vent hole) and the internal pressure on the tank's wall is based on its stored liquid column height.
An atmospheric storage tank is called closed type when it communicates with the environment through a neck containing a top opening (connection or nozzle) called an air vent. An atmospheric storage tank is called open type when it is neckless and communicates with the environment entirely through the full exposed surface of its stored liquid product.
The air vent of the closed type atmospheric storage tanks has the following functions:
To counterbalance the inside vacuum pressure that would be formed in the storage tanks, by allowing the free entry of atmospheric air. This free way entry may be due to a decrease in ambient temperature, that would consequently cause the contraction of air+gases mixture volume contained in the vapor space of the tanks and due to withdrawal operation of liquid product stored in the tanks. PA1 To counterbalance the internal pressure that would be developed inside the storage tanks, with free way blow out of air+gases mixture contained in the vapor space of the tanks through the vent hole due to an increase in the ambient temperature (consequently, the expansion of air+gases mixture volume contained in vapor space of the tanks would occur) and due to filling operation of liquid product to store in the tanks. PA1 a) By geometrical characteristics: PA1 b) By installation and using type: PA1 Water; PA1 Waste disposals (effluents and drainages); PA1 Chemical products; PA1 Petroleum and derivated products; PA1 Vegetable origin extracts; PA1 Animal origin extracts; PA1 Slurries of mineral processing. PA1 Combustible and/or flammable property; PA1 Chemical activity; PA1 Sanitary quality; PA1 Hygroscopic property; PA1 Odor, harmful to health and/or comfort of the people. PA1 Environment pollution; PA1 Fire and explosion hazard; PA1 Evaporation loss; PA1 Corrosion attack on neighboring construction and structures. PA1 Contamination of hygroscopic products; PA1 Water condensation in the vapor space of the tank that will cause: PA1 The operation mode of the presented device needs the aid of many operating accessories, and it depends on manipulation operations of the pressurization and depressurization systems. PA1 The device includes internal pressure control valves, making the tank slightly pressurized. PA1 The device keeps the vapor space of the storage tank hermetically closed; internal pressure change due to thermal variation of stored liquid product in the tank is transmitted to a plastic bag piece; the pressure of this bag piece is relieved to the environment through a pressure control valve. PA1 In the device, when the plastic piece is installed in the tank, the last one is kept fully charged with liquid product at its useful volume, and the first one is installed at the tank vapor space. PA1 There is water condensation at an inner side of the plastic piece, due to atmospheric air containing water vapor that is introduced and kept in the bag as the system is hermetically closed and does not allow water vapors to blow out of the bag. The structures requires that the device have a piping system with a suction valve to purge out condensed water from the inner side of the plastic piece. PA1 The devices consume energy and raw materials (gases); PA1 Constant vigilance is required during storage; PA1 Frequent maintenance is required; PA1 System start-up is vary hard and laborious; PA1 The purpose is only to eliminate evaporation losses of liquid products stored in atmospheric tanks. PA1 The breather bag allows normal air vent operation in atmospheric storage tanks with full segregation between stored liquid product and atmospheric air. PA1 The breather bag maintains atmospheric qualification of storage tanks in mechanical design procedures.
In this way, the mechanical strength design calculation of atmospheric storage tanks takes into account only the stress due to the height of stored liquid product in the tanks.
Atmospheric storage tanks are commercially available in a wide range of alternative forms, as:
a1) Closed type, with air vent hole, as: PA2 a2) Open type, with full exposed surface, PA2 b1) Fixed mounted pattern, as: PA2 b2) Mobile mounted pattern, as: PA2 Formation of water pocket in the liquid product; PA2 Water emulsion in stored liquid product.
Tank; PA3 Barrel; PA3 Drum; PA3 Lidded bucket; PA3 Bottle; PA3 Can. PA3 Pool; PA3 Basin; PA3 Lidless bucket; PA3 Open box. PA3 Outdoor; PA3 Indoor; PA3 Buried (underground). PA3 Part of engine system and/or aggregated to carrying vehicle, for: PA4 Road way transport (as car); PA4 Rail way transport (as train); PA4 Water way transport (as ship); PA4 Air way transport (as aircraft). PA3 Shaped for handling and transportation (as container); PA3 Skid-mounted type.
The atmospheric storage tanks are normally used for storing liquid products of several natures, as:
The liquid products to be stored in atmospheric tanks may present some characteristics, with specific applicable requirements concerning quality and security to be observed in each case, such as:
The liquid product is naturally subject to evaporation when gases are detected from the liquid gas separation surface. These gases are expelled through the air vent to the environment. This normally occurs for a dead state, and, more markedly, during the filling operation of the product in the atmospheric tank, by causing serious inconveniences like:
The atmospheric air which contains water vapors in its composition enters into the storage tanks through the vent and may cause several other problems, such as:
The communication between existent storage tanks and the environment by a free way through a vent hole, allows the entry into tank of insects, small animals or birds. These small creatures, when confined inside the tanks, may contaminate stored liquid product either by their excrement or via putrefaction of the bodies of dead animals, which have obviously been trapped in the tanks for a little too long. In this case, if there is a sanitary requirement of the liquid product, the contamination may forbid use of the liquid for consumption in food or pharmaceutical uses.
The PCT document number WO 84/04515, dated Nov. 22, 1984 and entitled Method and Device for Permanently Storing Liquids Particularly Volatile Liquids into Containers Closed Under Atmospheric Pressure, explains a process and a device that is applicable only to volatile liquid storage tanks, characterized in that the mass of the stored product is constant, under atmospheric pressure, in a closed-type storage system. The purpose of these devices is the elimination of product losses that occur through the tank's vent hole, because of either liquid product evaporation or its volume change, the latter one caused by product thermal variation.
The following points can be noted in the referenced document:
Another PCT document, number WO 85/01035, dated Mar. 14, 1985 and entitled Process and Device For Eliminating Losses Due to the Filling and Vapor Evolution in the Case of Volatile Substances Stored in Horizontal Cylindrical Tanks, explains a process and a device with specific application in cylindrical horizontal tanks, whose purpose is to eliminate the evaporation losses of stored products through the vent hole, during tank filling operation and by natural evaporation.
Like the earlier document, this device is also applicable specifically in storage tanks for volatile liquid products only, and so that the presented process has a pressurization and depressurization system too. The device has a plastic piece like a bag, hermetically closed inside the tank, attached to a blind flange at a top connection of the tank and joined to a pressurization and depressurization piping system. It complements the tank's other internal parts.
This plastic piece is inflated in the interior of the tank by using a gaseous material. Before its installation the vapor space of the tank is made inert using Halon gas. The normal operation of this device depends on low pressure nitrogen gas in the bag.
As noted with the first device, inside the plastic piece of the device, condensation of water vapors from atmospheric air will also occur. The presence of atmospheric air is due to its entry in the bag during operation. To purge out the condensed water, a suction valve connected to a piping system is needed.
On the other hand, the existing inner casing pipe allows evaporation of a small fraction of stored liquid proportional to its sectional area. Consequently, this device's efficiency is not 100% for avoiding liquid product evaporation loss.
In summary, it is possible to assert that processes and devices disclosed in document numbers WO 84/04515 and WO 85/01035 present the following inconveniences: